x86 stack alignment redux

[Dave Love]

It's a while since I tried to get something like this in for the
benefit of people doing double precision fortran calculations, at
least...

With this change, a glibc2-based system such as is now apparently
becoming usable, and -malign-double, g77 users running on GNUish
686-based boxes should no longer suffer an average 50% perfromance hit
because doubles on the stack only get word-aligned (or a smaller hit
on 586).  Previous discussion suggested it's a bug if STACK_BOUNDARY
doesn't agree with the initial stack pointer alignment and glibc2
ensures initial double alignment.

This really is important to serious scientific users with high-profile
projects of the sort I understand have just been slagging off g77/gcc
at a high-performance computing meeting here.

1997-11-13  Dave Love  <d.love@dl.ac.uk>

	* config/i386/linux.h (STACK_BOUNDARY): Define as 64 for glibc2.
	* config/i386/gnu.h (STACK_BOUNDARY): Define as 64.

*** config/i386/linux.h	1997/11/02 15:23:02	1.1
--- config/i386/linux.h	1997/11/13 16:45:40
***************
*** 37,42 ****
--- 37,48 ----
  #undef DEFAULT_PCC_STRUCT_RETURN
  #define DEFAULT_PCC_STRUCT_RETURN 1
  
+ #ifndef USE_GNULIBC_1
+ #undef STACK_BOUNDARY
+ #define STACK_BOUNDARY 64       /* glibc2's crt ensures this, libc5
+                                    only gives you 32 */
+ #endif
+ 
  /* This is how to output an element of a case-vector that is relative.
     This is only used for PIC code.  See comments by the `casesi' insn in
     i386.md for an explanation of the expression this outputs. */
*** config/i386/gnu.h	1997/11/13 16:46:29	1.1
--- config/i386/gnu.h	1997/11/13 16:47:18
***************
*** 3,8 ****
--- 3,11 ----
  /* This does it mostly for us.  */
  #include <i386/linux.h>
  
+ #undef STACK_BOUNDARY
+ #define STACK_BOUNDARY 64       /* glibc2's crt ensures this */
+ 
  #undef CPP_PREDEFINES
  #define CPP_PREDEFINES GNU_CPP_PREDEFINES("i386")